Endocrine & Reproduction Lecture Review

These flashcards review key concepts from hypothalamic-pituitary axes, thyroid function, insect hormones, reproduction strategies, gametogenesis, fertilization blocks, and sex determination covered in the lecture.

What vascular structure physically links the hypothalamus to the anterior pituitary?

The hypophyseal portal system—a pair of capillary beds connected by portal veins.

Which two capillary beds make up the hypophyseal portal system?

Capillary bed #1 in the median eminence of the hypothalamus and capillary bed #2 inside the anterior pituitary.

What is the main difference between releasing and inhibiting hormones from the hypothalamus?

Releasing hormones stimulate anterior-pituitary secretion; inhibiting hormones block it.

How many key releasing hormones were highlighted, and what are they?

Four: TRH, GnRH, CRH, and GHRH.

TRH from the hypothalamus triggers the anterior pituitary to release which hormones?

Thyroid-stimulating hormone (TSH) and prolactin.

Which anterior-pituitary hormones are released in response to GnRH?

Luteinizing hormone (LH) and follicle-stimulating hormone (FSH).

CRH stimulates the anterior pituitary to secrete what hormone?

Adrenocorticotropic hormone (ACTH).

GHRH stimulates the release of which anterior-pituitary hormone?

Growth hormone (GH).

What defines a tropic (tropin) hormone?

A hormone that targets another endocrine gland and induces it to secrete its own hormone.

List four classic tropic hormones released by the anterior pituitary.

TSH, LH, FSH, and ACTH.

Why aren’t growth hormone and prolactin classified as tropic hormones?

Because their primary targets are non-endocrine tissues and they do not mainly trigger another hormone’s release.

Why is the posterior pituitary considered "not a true gland"?

Its hormones (ADH and oxytocin) are synthesized in hypothalamic cell bodies and only stored/released in the posterior pituitary.

Name the two hormones released from the posterior pituitary.

Antidiuretic hormone (ADH) and oxytocin.

What is the principal action of ADH?

Reduces water loss by increasing water reabsorption in kidney collecting ducts.

Give two physiological roles of oxytocin.

Stimulates uterine contractions during labor and promotes milk ejection; also involved in social/maternal bonding.

How do the hypothalamus and posterior pituitary communicate?

Through long axons of neurosecretory cells—no portal vessels are needed for signal delivery.

In the abbreviations HPA, HPG, and HPT axis, what do the letters stand for?

H = hypothalamus, P = pituitary, third letter = target gland (A adrenal, G gonad, T thyroid).

What two cell types form a thyroid follicle?

Follicular epithelial cells (wall) and colloid (central storage of thyroglobulin).

Why is iodine essential for thyroid function?

Iodine atoms must attach to thyroglobulin to produce active T3 and T4 thyroid hormones.

What distinguishes T3 from T4?

T3 has three iodines; T4 has four (and is the more active circulating form).

What does TSH binding stimulate follicular cells to do?

Endocytose colloid, cleave thyroglobulin, and release T3/T4 into the bloodstream.

Which thyroid cells secrete calcitonin?

Parafollicular (C) cells located between follicles.

What primary dietary deficiency leads to endemic goiter?

Inadequate iodine intake.

Why does iodine deficiency cause thyroid enlargement (goiter)?

Lack of T3/T4 fails to inhibit TSH, causing excess TSH-driven colloid buildup and follicle swelling.

Define hyperthyroidism versus hypothyroidism.

Hyperthyroidism = overactive thyroid hormone output; hypothyroidism = underactive production (e.g., from iodine lack).

Which insect hormone is released from neurosecretory cells and targets the prothoracic gland?

Prothoracicotropic hormone (PTTH).

What does ecdysteroid (molting hormone) trigger in insects?

Molting by loosening the epidermis–exoskeleton connection.

How does juvenile hormone influence insect development?

Its declining concentration determines the transition from larval molts to the pupal/adult stage.

Name two common modes of asexual reproduction in animals.

Budding and fission.

State one major advantage of asexual reproduction.

Rapid population increase while retaining successful gene combinations.

State one major disadvantage of asexual reproduction.

Low genetic diversity, reducing adaptive potential in changing environments.

What is parthenogenesis?

Development of an unfertilized haploid egg into an individual (often with genome doubling).

Why are whiptail lizards notable for parthenogenesis?

All individuals are female, but hormone-driven pseudosexual behaviors still trigger egg activation.

List two energetic disadvantages of sexual reproduction.

Energy spent locating mates and risks from competition/courtship.

Give two evolutionary advantages of sexual reproduction.

Creates genetic diversity for adaptation and dilutes harmful gene combinations.

How many haploid gametes result from one germ cell in spermatogenesis and oogenesis?

Four sperm; one mature egg plus polar bodies.

What are Sertoli (nurse) cells, and where are they found?

Somatic cells lining seminiferous tubules; they nourish developing sperm and secrete regulatory hormones.

Trace the path of sperm from formation to storage.

Seminiferous tubules → rete testis → epididymis (maturation) → vas deferens.

Name four key parts of a mature sperm cell.

Acrosome, nucleus, midpiece packed with mitochondria, and flagellar tail.

What is a follicle in the ovary, and how is the dominant follicle chosen?

An egg plus surrounding somatic cells; the follicle that expresses most hormone receptors becomes dominant.

Which pituitary hormone surge induces ovulation?

A sharp increase in luteinizing hormone (LH).

Define external fertilization (spawning).

Gametes are released into the environment (usually water) where fertilization occurs outside the body.

What is the fast block to polyspermy in sea-urchin eggs?

Rapid depolarization of the egg membrane via Na⁺ influx, repelling additional sperm.

Describe the slow block to polyspermy.

Ca²⁺-triggered exocytosis of cortical granules creates a fertilization envelope that physically separates other sperm.

Which reptiles exhibit temperature-dependent sex determination, and how does temperature bias sex?

Many turtles and crocodilians; cooler nests often yield males, warmer nests females.

What is sequential hermaphroditism? Give an example.

Individuals change sex during life; clownfish switch from male to female when the dominant female dies.

What type of hermaphroditism do earthworms display?

Simultaneous hermaphroditism—each worm has functional male and female organs at the same time.